Tailor
it to the position and company to which you are applying; in other words,
a cover letter shouldn't be "canned."

Begin
by explaining why you are writing to this person and where you heard about
the job opening. You should include something like "Your job
announcement on govtjob.net. caught my attention."

Be
sure to say why you think you would be a good match for the position. If
the advertisement lists several traits or skills the employer wants to see
in job applicants, refer to those skills in your letter and say how you
exemplify them.

Mention
traits that will set you apart from other candidates.

Refer
the employer to your resume. You may include a phrase, such as:
"During your review of my resume, you may note that my background
contains the qualifications and experience you are looking for." This
will be a way to reinforce that your qualifications match the job profile.

Write
in a business-like but not overly formal manner; use your own wording.

Don’t
be too pushy. While it is acceptable to state that you are looking forward
to meeting the recruiter to explore the position in a personal interview,
don’t be presumptuous or state that you will contact the person to arrange
an interview.

Thank
the person for his/her time and attention to your application.

Remember
to sign your cover letter.

Note
"enclosure" or "enc." two lines after your signature
because your resume is enclosed.